The invention relates to a hollow needle having a duct, which comprises an aperture in the region of the needle point. Such needles are used in medicine, for example for injecting and for aspirating, such as the introduction of fluids. The invention also relates to a method for the manufacture of such hollow needles.
The points of conventional hollow needles, such as injection cannulae, are, in simple terms, sharply ground steel tubes. A sharp outer bevel edge, which permits a smooth injection technique, is produced by bevel grinding, for example. However in this case a rear bevel cutting edge, when seen in the direction of puncture, which is just as sharp, is simultaneously produced on the inside of the cannula, i.e. on the edge of the duct, the inner eye, and this can result in skin and tissue lying beneath it being punched out and getting inside the injection cannula.
This may result in the needle duct becoming blocked, in sensitive tissue structures which do not regenerate easily, such as nerve fibers, being damaged, and/or in infected pieces of skin which have been punched out being transmitted into deeper or other tissue structures or layers, and this can result in syringe abscesses.
The shortcomings of the conventional needle point are known. As early as 1891 H. I. Quincke described an improved spinal needle named after him, which is still used today for lumbar puncture. Quincke's spinal needle has a precisely adapted guide (obturator/filling body/insertion rod), which protects the inner lumen of the injection cannula from the ingress of punched out material, e.g. tissue or membrane material. After puncture, the guide is removed, and the liquor fluid can be drawn up without any problems.
In 1898 during the spinal anaesthesia performed for the first time as a self-experiment, A. Bier recongnized that the loss of liquor fluid through the puncture wound in the dura/arachnoidea (also called meninges, or the meninx or spinal meninx) can result in a severe postspinal headache. The frequency of postspinal headache is dependent on the diameter of the needle and the type of needle point, together with the age, sex and individual predisposition. In 1922 R. Hoyt pointed out the significance of needle diameters and described the two needle technique, in which a thicker needle is firstly inserted as an "introducer" (insertion aid), and a smaller needle is advanced through this introducer right into the subarachnoid space. The puncture wound of the dura/arachnoidea remains limited by this, and the headache rate is reduced. In 1926 H. M. Greene described a "round ground" (plain ground) needle point, which carefully forces the fibers of the dura and arachnoidea apart, but does not split them, as is the case with the conventional Quincke needle having the sharp outer bevel edge. A further development of the "atraumatic spinal needle" was described in 1951 by Hart and Whitacre: a needle with a closed needle point like the point of a pencil with a lateral aperture into said point. This needle was further improved by Sprotte in 1987 by enlarging the lateral aperture so as to prevent a nozzle effect when injecting the local anaesthetic into the liquor.
In 1944 E. B. Tuohy described the method of continuous spinal anaesthesia. For puncture he used a so-called Huber cannula, an injection cannula having a curved point. The curve is formed so that the bevel plane of the needle point can be guided parallel to the cannula. This results in that the rear bevel cutting edge of the cannula point can be hidden behind the curve, and as a result the risk of punching out tissue is reduced, but not eliminated. In 1957 R. S. Wagner Jr. improved the Huber cannula by reducing the bending radius at the needle point and as a result he achieved better control of the bevel plane parallel to the cannula and reduced the length of the bevel eye. The more precise positioning of the needle point was achieved by this. In 1958 P. A. Cheng modified the curved needle point again by blunting the front bevel cutting edge and guiding the bevel plane with a slight angle to the cannula plane. However in all the above-specified designs the rear bevel cutting edge remains sharp. Therefore to reduce the risk of tissue being stamped out during puncture, an adapted guide, which covers the rear bevel cutting edge, i.e. the edge of the aperture, is introduced into the needle.
In 1989 H. Haindel and H. Muller described a cannula having a concave bevelled point, which does not punch out tissue to a great extent (Biomed. Technik, 34 (1989), 79-84), in which the rear edge of the aperture of the duct is blunted with a special glass bead ray treatment. The bead ray treatment can result in residue in the duct, which is very difficult to remove. The bead ray treatment, which does not permit a specific and selective treatment of the rear, inner bevel cutting edge, may result in only an unsatisfactory inner rounding of the edge of the aperture being achieved.
The use of this cannula is recommended for the protection of the silicone membrane of portable systems (to receive the injection fluid from membrane-sealed containers, the membrane is perforated with the needle/the container can be implanted). With its use in other puncture techniques (anaesthesia, neurosurgery, radiology) in tissue which is less consistent than silicone rubber, parts of tissue are punched out. This is the case in particular when puncturing nerve tissue, which has less inherent elasticity and consistency.
A cavity needle having a point in the shape of a pencil point, in which the cannula aperture is laterally mounted in the cylindrical part, is referred to as "Sprotte needle". The aperture of the duct is relatively far away from the point in the Sprotte needle. The Sprotte needle is also used with a guide so as to prevent the penetration of tissue particles into the cannula aperture. Therefore it is practically impossible to use it during punctures which have to guarantee a free backflow of fluid through the needle during puncture. The lateral aperture of the duct, the cannula eye, represents a weak point in the cannula and there is a risk of the cannula bending or even the hollow needle breaking when it comes into contact with bone.
From the medical point of view, the punching out of tissue particles is associated with an increased tissue trauma for the patient and is therefore undesirable. This is particularly the case if the cannula has to be introduced into tissue which does not easily regenerate, such as nerves (conduction anaesthesia) or brain (neurosurgery).
When steroids are injected, which impair the immune defense system, the transmission of stamped out particles of skin into other tissue layers can result in dreaded syringe abscesses. The location and positioning of cannulae in tissue structures, in which the position of the hollow needle is verified and controlled by means of fluid which freely flows back (blood, liquor, lymph, synovial fluid, bile, discharges, accumulation of pus, etc.), is hampered if the lumen/the duct is restricted or even blocked by tissue parts or in any other way. A multiple puncture is the necessary consequence, frequently associated with tissue trauma and an increase in pain for the patient.